1. The Field of the Invention
This invention relates generally to electrical devices for tracking items in the possession of a person, and more particularly to a system in which a first electrical device can selectively communicate with at least one other electrical device and can indicate a presence and/or location of the other device.
2. The Background Art
Various devices are known in the art for monitoring or locating objects that are commonly found in possession of a person. For example, in U.S. Pat. No. 5,680,105 a lost object locator includes activation units that are mounted on a rack and response units that are attached to objects that are commonly misplaced such as car keys. Each of the activation units corresponds to a single response unit and when one of the objects that has a response unit attached thereto is lost or misplaced, the corresponding activation unit can be activated to send a signal to the response unit on the lost object. When the response unit attached to the lost object receives the signal from the activation unit, an audible tone is emitted from the response unit which, ideally, will indicate the location of the lost object to the person activating the activation unit. The invention also provides for mobile activation units that can be placed in areas that the person believes are nearer the lost object so that the audible tone can be easily detected by the person when the response unit is activated by the activating unit. Undesirably, however, an activation unit is required for each object that is to be located and the activation unit provides only a single function for locating the lost object. Further, although the lost object locator provides for a master activation unit that can be detached from the rack when a person is looking for lost objects, the master activation unit suffers from a lack of programmability and individual control for interacting with objects. For example, the master activation unit is incapable of selectively activating individual response units. Finally, the response units are incapable of locating a lost or misplaced activation unit.
Another device for monitoring or locating objects is the child proximity detector disclosed in U.S. Pat. No. 5,646,593. The child proximity detector includes a parent unit that receives pulse signals on a regular interval from a child unit. When the parent unit fails to receive a signal from the child unit, an alarm condition is established in the parent unit. Because these detectors can be "fooled" by causing a parent unit to fail to reach an alarm state when the child unit is out of range, those skilled in the art have developed parent and child units that communicate with each other. However, even these improved "intelligent" units suffer from the disadvantage of having limited functionality because a person cannot dynamically modify a parent unit to implement individual control over a single child unit, e.g., the units can not be programmed to selectively activate a single child unit. Furthermore, the child unit cannot two be used to locate the parent unit.
Yet another device of the prior art disclosed in U.S. Pat. No. 5,621,388 provides the function of a child proximity detector by monitoring a person, or persons, to determine if they have moved, or been moved, further than a preselected distance from a base station. Although this device provides dual functionality in the parent device of both monitoring and locating a person wearing a remote (i.e., child) device, the device has drawbacks for use as a possession tracker because it does not offer more than two functions. One drawback of only having dual functionality is that the system will not operate in a locating mode unless the remote device is located outside the preselected distance set in the parent device. The prior art device also lacks the ability to selectively activate remote devices with the parent device. In addition, this prior art device does not have the capability to automatically detect when it should shut down to avoid interfering with other signals, e.g., when it is near a transponder on a commercial airline during take off. Further, the remote device will not operate in a manner to locate the parent device.
In view of the foregoing, it would be advantageous to provide a system having a local (i.e., parent) device that can be selectively programmed by a person to track one or more remote (i.e., child) devices, wherein the remote device can also operate to locate the local device, and wherein the system will automatically detect when communication signals between the devices should not occur and thus shut down communications.